Tuesday, February 4, 2014

Allview Speed City/Onda 701 touch screen replacement

After about a year of use (and some hard drops) the touchscreen in my Allview Speed City tablet (Onda 701 clone) stopped working in a 1/3 region of the screen. I could still use the tablet by rotating it when I needed to tap in the broken area, but I needed to replace the touchscreen.

The disassembly (and reassembly process) took me about 2 hours, but was not very difficult. The first thing to do is to remove the rubber caps on top of the screws in the back of the tablet (use a needle/pincer). You can unscrew the screws (small phillips head).

The tablets back cover is glued on (the screws don't hold it actually). You will need something like a credit card to separate the back cover from the tablet chassis.

Next, you can separate the screen unit from the chassis by inserting the credit card between them (start with a side). The screen detaches quickly once you manage to separate one clip.

At this point I still had the tablet turned on and I could test the connectors (to see if the touchscreen connector was loose). I took out the connector and replaced it with the new touch screen and tried out the new touch screen before removing the old one.

Here are some more images of the tablet's internals:

Mainboard overview

Processor and RAM

Internal storage FLASH chip and screen (left) and touchscreen (right) connectors. In the bottom left you can see some solder points for something that looks like a serial port (haven't tested it).

Top part - camera connection and radios (you can see a Realtek chip)

When you are ready, detach the touchscreen + screen from the mainboard (2 connectors). The touchscreen is glued onto the screen and it will take a while to detach. Use a knife and start at a corner. As you can see, the touchscreen has 2 layers - a transparent plastic on top and an adhesive plastic between the top and the screen. You will need to detach the adhesive plastic completely! It may look like glass, but it's not. You should not be able to cut yourself in it, but take care because it breaks into small shards.

Touchscreen layers. You can see some of the circuitry for the touch sensors

Old touchscreen detached (and broken in the process). Some debris are left on the screen mount.

Once the top comes off you can add the new touchscreen (after you've cleared all the residues from the panel. Before gluing the top on, make some alignment tests - you want the touchscreen to be perfectly aligned on top of the screen. Prior to the attachment make sure to clean both the screen and the back side of the touchscreen with a cloth to remove any finger marks or debris.

Try out to position and align the touchscreen correctly before removing the white bands

Remove the paper protections on the new touchscreen and glue it on the screen mount. Once it is glued on, connect the ribbon cables back to the motherboard and try it out. If everything is ok, reassemble the tablet (you may need to use some glue to hold the back case in place).

Overall the operation is not difficult to perform. The end result was satisfying, but the replacement touchscreen has some "blind spots" - regions where it doesn't easily register touch events. I could see these spots before when testing the new touchscreen. In terms of alignment I was about 1.5mm off (the touchscreen is about 1.5mm too high), and I have a small open region in the bottom of the tablet. It doesn't impact functionality in any way.